1. Field of the Invention
This invention relates to sealing agents comprising compounds having free isocyanate groups and to a new process for the sealing of constructions by using these sealing agents.
2. Description of the Prior Art
Various processes have been developed in structural engineering for sealing fissures and leaks in constructions. The simplest method is the use of a pressed-in mortar based on cement/water suspensions. Such suspensions are used for injecting into loose rock floors and fissures, into rock concrete or into brickwork. However, it is no longer practically feasible to compress fissure widths of less than 3 mm using cement emulsions, because the fine cement particles which settle on the sides of the fissure render a faying compression of deep fissures impossible. Injection resins have been developed for compressing fine fissures of less than 3 mm in width and these resins have varying functions. Two areas of use may generally be distinguished: the force-locking bonding of cracked constructions and the sealing of cracked or water-permeable structural elements.
The working method applied is thereby one and the same, the difference lies only in the type of compressed materials. In the case of force-locking bonding, materials are required which have high mechanical strengths and good adhesion characteristics. In this process, a thinly liquid epoxide resin, for example, is pressed into fissures and cavities of the construction using pressures as high as 200 bars, so that after the resin has hardened, a monolithic cohesion again results.
On the other hand, in the case of sealing water-permeable structural elements, materials are required whose hardening is furthered or is at least not disturbed by moisture, which contract minimally during hardening and which have a certain elasticity. Another purpose of use of injection resins arises from the necessity to protect the steel in steel concrete constructions from corrosion. According to current prior art, fissure widths of 0.2 mm are considered harmless for corrosion of the steel under favorable conditions; however, under unfavorable conditions, e.g. under the influence of corrosion-promoting materials, this limit may fall to 0.1 mm. The working procedure comprises the following steps:
1. Injection holes are bored approximately every 10 to 50 cm down to the required injection depth. PA1 2. The fissures on the concrete surface are sealed, e.g. by synthetic resin mortar. PA1 3. So-called packers are inserted into the injection holes. These devices are non-return valves which are self-sealing, when screwed in, by virtue of a rubber collar. PA1 4. The tubes for the pressure reservoir are connected to the packers and the resin is injected with compression until it issues at the neighboring points. PA1 (a) from about 0 to 5% by weight of 2,2'-diisocyanato-diphenyl methane; PA1 (b) from about 20 to 80, preferably from about 30 to 70% by weight of 2,4'-diisocyanato diphenyl methane; and PA1 (c) from about 80 to 20, preferably from about 70 to 30% by weight of 4,4'-diisocyanato diphenyl methane and/or higher than difunctional polyisocyanates of the diphenyl methane series.
Whereas for the force-locking joins, liquid, cold-hardening epoxide resins are frequently used, polyurethane resins are often used for the sealing procedure.
The known polyurethane binders are formed by mixing a polyisocyanate with a polyhydroxyl compound, whereby the two components react together to form a urethane. Where water is present in the formations to be sealed, carbon dioxide gas evolves as the result of a subsidiary reaction and this gas causes an increase in volume of the sealing resin which is required in this case. Since water is probably present in any case in the constructions to be sealed, even a building material such as concrete which appears to be dry still contains a residual moisture of at least 3.5%, the carbon dioxide gas evolution is a necessary and a chemically-conditioned feature of the sealing procedure.
Investigations should particularly be made from today's point of view of comprehensive environmental hygiene as to what extent ground water, or in certain cases also drinking water, may be contaminated by the synthetic resins injected. Those resins containing solvent might therefore be judged unfavorably. German Offenlegungsschrift No. 2,851,313 and Austrian Pat. No. 259,190 describe insulating liquids containing isocyanate with from 20 to 60% of diisocyanate, whereby the remainder consists of solvent mixtures. The fact cannot be ruled out that some of these solvents pass into the ground water by diffusion and contaminate it. This applies similarly to the preparations containing isocyanate and described in German Auslegeschrift No. 1,914,554 (corresponding to U.S. Pat. Nos. 3,623,330 and 3,798,186) which are to be used for sealing floor formations and underground constructions. In the case of two component systems consisting of mixtures of polyisocyanates and polyols, a separation of the two components before the chemical reaction between the two components is completed must be taken into consideration during injection into foundations through which ground water flows. Among other reasons, this is due to the fact that the water-miscibility or water-solubility of the two components is very different. Therefore, in two component systems, the transition of at least one component into the ground water cannot be discounted.
A further criterion for the assessment of sealing resins is the shrinkage which occurs after hardening. An adequate volume-stability is required after completion of the chemical reaction, whereby a shrinkage extent of from about 10 to 15% may be tolerated. The volume-stability of the hardened synthetic resin is important in that a permanent sealing is required which must not be endangered by volume contraction of the sealing resin. It is obvious that isocyanate derivatives containing solvent may not be volume-stable through evaporation of the solvent.
A sufficiently low viscosity is naturally necessary for the suitability of isocyanate resins for fissure compression, so that the transport of the sealing resin in the construction constitution may take place rapidly enough.
This invention is therefore directed to providing a new process for the sealing of constructions, in which sealing agents are used which only contain one binder component to avoid contamination in the ground and drinking water with extensive elimination of solvents and which also only exhibit slight shrinkage after hardening.
This object may be achieved by the process according to the invention which is described in more detail in the following.